How Evaporation Lines vs. Faint Positive Results Look

Clearing up the confusion about at-home pregnancy tests

Reading your at-home pregnancy test result can be tricky. How can you tell whether that subtle, extra line is a positive result—or something else?

An evaporation line (or evap line) typically appears like a faded streak, while a faint positive test result looks like a lighter blue or pink line, depending on the test dye color.

This article provides an overview of home pregnancy test results.

A woman holding a pregnancy stick

HUIZENG HU / Getty Images

Differences Between Evaporation Lines vs. Faint Positives

At-home pregnancy tests include what's known as a control line, which is a line to confirm that the test is working, and a test line, which provides the results. Sometimes evaporation lines and faint positive result lines can appear similar, especially if you don't know exactly what you're looking for.


It's helpful to take a closer look at the line's color. Is there a faint color to the line that's the same shade as the control line (usually blue or pink)? This is probably a faint positive result.

If the line appears more "colorless," like gray, white, or shadowy, this is likely an evaporation line.

Thickness or Thinness of Line

Consider whether the line in question is roughly the same size as the control line. Is it the same thickness and does it run from top to bottom?

If the answer to these questions is yes, even though the line may not be as dark as the control line, it's likely a faint positive.

If the line you're looking at is a different size and shape or doesn't expand across the entire length of the test window, an evaporation line might be to blame.

How Long It Takes to Appear

There's a reason why it's important to read your pregnancy test within the time frame that's noted on the product's instructions (usually somewhere from three to 10 minutes). When urine sits on the test for too long past the reaction time, it'll dilute and dry out—causing an evaporation line.

If you're checking the result during the window, it's more likely to be a faint positive result. But if you notice the additional line later that day, it's probably an evap line.

How Dye Works in a Pregnancy Test

Home pregnancy tests (dye-based and digital) check your urine for human chorionic gonadotropin (hCG). The dye-based tests work by chemically reacting—and changing color—when hCG is present.

How Common Are Evaporation Lines?

Evaporation lines can be common on home pregnancy tests, but they’re not often discussed.


An evaporation line happens when the pregnancy test is read after the time frame specified in the instructions.

Many at-home pregnancy tests suggest reading the results within two, five, or up to 10 minutes after urinating on the stick. Checking results after that window means your urine has dried up, potentially causing that streaky evap line.

Like pregnancy tests, reading at-home COVID-19 tests can also prompt confusion. Does it matter how faint or thin the test result line is? Experts say the faintness or darkness of the test line—and how long it takes to appear—indicate how sick you are and how likely the virus is to be transmitted to other people.

Getting the Most Accurate Pregnancy Test Results

When taking at-home pregnancy tests, several factors go into getting the most accurate result and avoiding confusion. Experts recommend the following tips:

  • Check your results within the recommended reaction time window, which will vary slightly by pregnancy test brand.
  • Try a digital at-home pregnancy test instead of a dye-based one if you're concerned about evaporation lines.
  • Test first thing in the morning because your urine is more likely to have higher levels of hCG at that time.
  • Wait until a day after your missed period to test, even though some pregnancy tests are sensitive enough to detect pregnancy earlier than a missed period.

Though many pregnancy test manufacturers market their products as extremely accurate, research suggests that real-life situations likely affect the accuracy rate.

Next Steps After a Faint Positive Result

You might consider retaking the at-home test to ensure the result if you think it may be a faint positive.

After that, the next step is to check with a healthcare provider to schedule an in-office appointment. They can confirm pregnancy via ultrasound or blood test, if needed, during this visit.


An evaporation (or evap) line is a slight, typically colorless streak on an at-home pregnancy test that can cause confusion. These lines usually show up when you've read the results outside the suggested window and the urine has dried. On the other hand, a faint positive test result will be the same color as the control line—just not as bold or dark. This is more likely to be the case if you look at the test results within the suggested time frame.

If unsure about your at-home pregnancy test results, try testing again the next day. From there, call a healthcare provider if your test is positive or if you need more help getting an accurate reading.

Frequently Asked Questions

  • How dark or light is an evap line?

    An evap line is a faint streak that's so light it may look gray or almost colorless. It's not as dark or bold as the control or positive result lines.

  • Why does a negative pregnancy test turn positive?

    This is probably a false positive test result, particularly if you look at a test result outside the indicated window. By that time, your urine has dried, and the reaction time for the test is up, which can lead to evaporation lines or other changes that likely do not mean a positive result.

  • Does an evap line mean pregnancy?

    An evap line does not indicate pregnancy. The safest bet is to take another test and read it within the specified time frame for the most accurate reading. Check with a healthcare provider if you're still unsure about the results.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  7. U.S. Food and Drug Administration. Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - guidance for industry and FDA reviewers/staff.

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By Cristina Mutchler
Cristina Mutchler is an award-winning journalist with more than a decade of experience in national media, specializing in health and wellness content.